Electrode for secondary battery, preparation thereof, and secondary battery and cable-type secondary battery comprising the same

ABSTRACT

A sheet-form electrode for a secondary battery includes a current collector; an electrode active material layer formed on one surface of the current collector; a porous organic-inorganic layer formed on the electrode active material layer and including inorganic particles and a polymer binder; and a first porous supporting layer formed on the porous organic-inorganic layer. The sheet-form electrode for a secondary battery has supporting layers on at least one surface thereof to exhibit surprisingly improved flexibility and prevent the release of the electrode active material layer from a current collector even if intense external forces are applied to the electrode, thereby preventing the decrease of battery capacity and improving the cycle life characteristic of the battery.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No.PCT/KR2014/004047 filed on May 7, 2014, which claims priority under 35USC 119(a) to Korean Patent Application No. 10-2013-0051565 filed in theRepublic of Korea on May 7, 2013, and Korean Patent Application No.10-2014-0054279 filed in the Republic of Korea on May 7, 2014, thedisclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an electrode for a secondary battery,more specifically to an electrode for a secondary battery which can beprevented from the release of an electrode active material layer andhave improved flexibility, a method of preparing the electrode, and asecondary battery and a cable-type secondary battery comprising theelectrode.

BACKGROUND ART

Secondary batteries are devices capable of storing energy in chemicalform and of converting into electrical energy to generate electricitywhen needed. The secondary batteries are also referred to asrechargeable batteries because they can be recharged repeatedly. Commonsecondary batteries include lead accumulators, NiCd batteries, NiMHaccumulators, Li-ion batteries, Li-ion polymer batteries, and the like.When compared with disposable primary batteries, not only are thesecondary batteries more economically efficient, they are also moreenvironmentally friendly.

Secondary batteries are currently used in applications requiring lowelectric power, for example, equipment to start vehicles, mobiledevices, tools, uninterruptible power supplies, and the like. Recently,as the development of wireless communication technologies has beenleading to the popularization of mobile devices and even to themobilization of many kinds of conventional devices, the demand forsecondary batteries has been dramatically increasing. Secondarybatteries are also used in environmentally friendly next-generationvehicles such as hybrid vehicles and electric vehicles to reduce thecosts and weight and to increase the service life of the vehicles.

Generally, secondary batteries have a cylindrical, prismatic, or pouchshape. This is associated with a fabrication process of the secondarybatteries in which an electrode assembly composed of an anode, acathode, and a separator is mounted in a cylindrical or prismatic metalcasing or a pouch-shaped casing of an aluminum laminate sheet, and inwhich the casing is filled with electrolyte. Because a predeterminedmounting space for the electrode assembly is necessary in this process,the cylindrical, prismatic or pouch shape of the secondary batteries isa limitation in developing various shapes of mobile devices.Accordingly, there is a need for secondary batteries of a new structurethat are easily adaptable in shape.

To fulfill this need, suggestions have been made to develop cable-typebatteries having a very high ratio of length to cross-sectionaldiameter. The cable-type batteries are easy in shape variation, whilebeing subject to stress due to external force for the shape variation.Also, the electrode active material layer of cable-type batteries may bereleased by rapid volume expansion during charging and dischargingprocesses. From these reasons, the capacity of the batteries may bereduced and the cycle life characteristics thereof may be deteriorated.

Such a problem may be solved in a certain degree by increasing theamount of a binder used in the electrode active material layer toprovide flexibility during bending or twisting. However, the increase ofa binder amount in the electrode active material layer causes anelectrode resistance rise to deteriorate battery performances. Also,when intense external forces are applied, for example, in the case thatelectrodes are completely folded, the release of the electrode activematerial layer cannot be prevented even though the amount of a binderbecomes increased. Therefore, this method is insufficient to solve suchproblems.

SUMMARY OF THE DISCLOSURE

The present disclosure is designed to solve the problems of the relatedart, and therefore the present disclosure is directed to providing anelectrode for a secondary battery which can be mitigated from crackgeneration in an electrode active material layer by external forces, andalso can be prevented from the release of the electrode active materiallayer from a current collector even if severe cracks are present, amethod of preparing the electrode, and a secondary battery and acable-type secondary battery comprising the electrode. In accordancewith one aspect of the present disclosure, there is provided asheet-form electrode for a secondary battery, comprising a currentcollector;

an electrode active material layer formed on one surface of the currentcollector; a porous organic-inorganic layer formed on the electrodeactive material layer and comprising inorganic particles and a polymerbinder, and a first porous supporting layer formed on the porousorganic-inorganic layer.

The current collector may be made of stainless steel, aluminum, nickel,titanium, sintered carbon, or copper, stainless steel treated withcarbon, nickel, titanium or silver on the surface thereof; analuminum-cadmium alloy; a non-conductive polymer treated with aconductive material on the surface thereof; a conductive polymer, ametal paste comprising metal powders of Ni, Al, Au, Ag Pd/Ag, Cr, Ta,Cu, Ba or ITO; or a carbon paste comprising carbon powders of graphite,carbon black or carbon nanotube.

Also, the current collector may be in the form of a mesh.

In addition, the current collector may further comprise a primer coatinglayer consisting of a conductive material and a binder. The conductivematerial may comprise any one selected from the group consisting ofcarbon black, acetylene black, ketjen black, carbon fiber, carbonnanotube, graphene and a mixture thereof.

The binder may be selected from the group consisting of polyvinylidenefluoride (PVDF), polyvinylidene fluoride-co-hexafluoro propylene,polyvinylidene fluoride-co-trichloroethylene, polybutyl acrylate,polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone,polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide,polyarylate, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof.

Further, the current collector may have a plurality of recesses on atleast one surface thereof.

The plurality of recesses may be continuously patterned orintermittently patterned, on at least one surface thereof.

The continuous patterned recesses may be formed with spacing apart witheach other in the longitudinal direction.

The intermittently patterned recesses may be formed by a plurality ofholes.

The plurality of holes may be a circular or polygonal shape.

Meanwhile, the first supporting layer may be a mesh-form porous membraneor a non-woven fabric.

The first supporting layer may be made of any one selected from thegroup consisting of high-density polyethylene, low-density polyethylene,linear low-density polyethylene, ultra-high molecular weightpolyethylene, polypropylene, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate,polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide,polyphenylene sulfide, polyethylene naphthalate, and a mixture thereof.

Also, the electrode may further comprise a conductive material-coatinglayer having a conductive material and a binder on the first supportinglayer.

In the conductive material-coating layer, the conductive material andthe binder may be present in a weight ratio of 80:20 to 99:1.

The conductive material may comprise any one selected from the groupconsisting of carbon black, acetylene black, ketjen black, carbon fiber,carbon nanotube, graphene and a mixture thereof.

The binder may be selected from the group consisting of polyvinylidenefluoride (PVDF), polyvinylidene fluoride-co-hexafluoro propylene,polyvinylidene fluoride-co-trichloroethylene, polybutyl acrylate,polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone,polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide,polyarylate, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof.

Meanwhile, the porous organic-inorganic layer may be formed from amixture of the inorganic particles and the polymer binder in a weightratio of 20:80 to 95:5.

Also, the porous organic-inorganic layer may have a pore size of 0.01 to10 μm and a porosity of 5 to 95%.

The inorganic particles may be inorganic particles having a dielectricconstant of 5 or higher, inorganic particles having the ability totransport lithium ions, or a mixture thereof.

Examples of the inorganic particles having a dielectric constant of 5 orhigher include BaTiO₃, Pb(Zr_(x)Ti_(1-x))O₃ (PZT, 0<x<1),Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT, 0<x<1, 0<y<1),(1-x)Pb(Mg_(1/3)Nb_(2/3))O₃-xPbTiO₃ (PMN-PT, 0<x<1), hafnia (HfO₂),SrTiO₃, SnO₂, CeO₂, MgO, NiO, CaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, SiC, SiO₂,AlOOH, Al(OH)₃, TiO₂ and a mixture thereof.

Also, examples of the inorganic particles having the ability totransport lithium ions include lithium phosphate (Li₃PO₄), lithiumtitanium phosphate (Li_(x)Ti_(y)(PO₄)₃, 0<x<2, 0<y<3), lithium aluminumtitanium phosphate (Li_(x)Al_(y)Ti_(z)(PO₄)₃, 0<x<2, 0<y<1, 0<z<3),(LiAlTiP)_(x)O_(y) type glass (0<x<4, 0<y<13), lithium lanthanumtitanate (Li_(x)La_(y)TiO₃, 0<x<2, 0<y<3), lithium germaniumthiophosphate (Li_(x)Ge_(y)P_(z)S_(w), 0<x<4, 0<y<1, 0<z<1, 0<w<5),lithium nitride (Li_(x)N_(y), 0<x<4, 0<y<2), SiS₂ type glass(Li_(x)Si_(y)S₂, 0<x<3, 0<y<2, 0<z<4), P₂S₅ type glass (Li_(x)P_(y)S₂,0<x<3, 0<y<3, 0<z<7) inorganic particles, and a mixture thereof.

The inorganic particles may have an average diameter of 10 nm to 5 μm.

Also, the polymer binder may be selected from the group consisting ofpolyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polybutylacrylate, polymethyl methacrylate, polyacrylonitrile,polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate,polyethylene oxide, polyarylate, cellulose acetate, cellulose acetatebutyrate, cellulose acetate propionate, cyanoethylpullulan,cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose,pullulan, carboxyl methyl cellulose, styrene-butadiene rubber,acrylonitrile-styrene-butadiene copolymer, polyimide and a mixturethereof.

The electrode may further comprise a porous coating layer formed on thefirst porous supporting layer and comprising a mixture of inorganicparticles and a binder polymer.

The electrode may further comprise a second supporting layer formed onanother surface of the current collector.

The second supporting layer may be a polymer film.

The polymer film may be made of any one selected from the groupconsisting of polyolefin, polyester, polyimide, polyamide and a mixturethereof. When the electrode for a secondary battery is used as an anode,the electrode active material layer may comprise an active materialselected from the group consisting of natural graphite, artificialgraphite, or carbonaceous material; lithium-titanium complex oxide(LTO), and metals (Me) including Si, Sn, Li, Zn, Mg, Cd, Ce, Ni and Fe;alloys of the metals; an oxide (MeOx) of the metals; a complex of themetals and carbon; and a mixture thereof, and when the electrode for asecondary battery is used as a cathode, the electrode active materiallayer may comprise an active material selected from the group consistingof LiCoO₂, LiNiO₂, LiMn₂O₄, LiCoPO₄, LiFePO₄, LiNiMnCoO₂,LiNi_(1-x-y-z)Co_(x)M1_(y)M2_(z)O₂ (wherein M1 and M2 are eachindependently selected from the group consisting of Al, Ni, Co, Fe, Mn,V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z are each independently anatomic fraction of oxide-forming elements, in which 0≦x<0.5, 0≦y<0.5,0≦z<0.5, and x+y+z≦1), and a mixture thereof.

In accordance with another aspect of the present disclosure, there isprovided a method of preparing a sheet-form electrode for a secondarybattery, comprising (S1) applying a slurry containing an electrodeactive material on one surface of the current collector, followed bydrying, to form an electrode active material layer, (S2) applying amixed organic-inorganic slurry containing inorganic particles and apolymer binder on the electrode active material layer (S3) forming afirst porous supporting layer on the mixed organic-inorganic slurrywhich is applied; and (S4) compressing the resultant obtained in step(S3) to form a porous organic-inorganic layer which is adhered betweenthe electrode active material layer and the first porous supportinglayer to be integrated with each other.

In the step (S3), forming a first porous supporting layer on the mixedorganic-inorganic slurry may be carried out before the binder polymer iscured.

In the step (S4), compressing the resultant obtained in step (S3) toform a porous organic-inorganic layer which is adhered between theelectrode active material layer and the first porous supporting layer tobe integrated with each other may be carried out before the binderpolymer is cured.

The method may further comprise forming a second supporting layer bycompression on another surface of a current collector; before the (S1)step or after the (S4) step.

Also, in accordance with yet another aspect of the present disclosure,there is provided a secondary battery comprising a cathode, an anode, aseparator interposed between the cathode and the anode, and anon-aqueous electrolyte solution, wherein at least one of the cathodeand the anode is the above-mentioned electrode for a secondary batteryaccording to the present disclosure.

The secondary battery may be formed as a stacking, winding,stacking/folding, or cable type secondary battery.

In addition, in accordance with yet still another aspect of the presentdisclosure, there is provided a cable-type secondary battery,comprising: an inner electrode; a separation layer surrounding the outersurface of the inner electrode to prevent a short circuit betweenelectrodes; and a outer electrode surrounding the outer surface of theseparation layer and formed by being spirally wound, wherein at leastone of the inner electrode and the outer electrode is formed using theabove-mentioned electrode for a secondary battery according to thepresent disclosure.

The outer electrode may be in the form of a uniaxially extended strip.

The outer electrode may be spirally wound so that it is not overlappedin its width.

The outer electrode may be spirally wound with space within the doublelength of its width so that it is not overlapped.

The outer electrode may be spirally wound so that it is overlapped inits width.

The outer electrode may be spirally wound so that the width of itsoverlapped part is within 0.9 folds of the width of the outer electrodeitself.

The inner electrode may be a hollow structure whose central part isempty.

One or more electrodes according to the present disclosure may bespirally wound as the inner electrode.

The inner electrode may be provided with a core of inner currentcollector, a core for supplying lithium ions, which comprises anelectrolyte, or a filling core therein

The core of inner current collector may be made of carbon nanotube,stainless steel, aluminum, nickel, titanium, sintered carbon, or copper,stainless steel treated with carbon, nickel, titanium or silver on thesurface thereof; an aluminum-cadmium alloy; a non-conductive polymertreated with a conductive material on the surface thereof; a conductivepolymer.

The core for supplying lithium ions may comprise a gel polymerelectrolyte and a support.

The core for supplying lithium ions may comprise a liquid electrolyteand a porous carrier. The electrolyte which is used in the core forsupplying lithium ions may be selected from a non-aqueous electrolytesolution using ethylene carbonate (EC), propylene carbonate (PC),butylenes carbonate (BC), vinylene carbonate (VC), diethyl carbonate(DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylformate (MF), γ-butyrolactone (γ-BL), sulfolane, methyl acetate (MA) ormethyl propionate (MP); a gel polymer electrolyte using PEO, PVdF,PVdF-HFP, PMMA, PAN, or PVAc; and a solid electrolyte using PEO,polypropylene oxide (PPO), polyether imine (PEI), polyethylene sulphide(PES), or polyvinyl acetate (PVAc).

The electrolyte may further comprise a lithium salt which may beselected from LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆,LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li,(CF₃SO₂)NLi, lithium chloroborate, lower aliphatic lithium carbonate,lithium tetraphenylborate, and a mixture thereof.

The filling core may be made of polymer resins, rubber and inorganics inthe form of a wire, a fiber, a powder, a mesh and a foam.

The inner electrode may be an anode or a cathode, and the outerelectrode may be a cathode or an anode corresponding to the innerelectrode.

Meanwhile, the separation layer may be an electrolyte layer or aseparator.

The electrolyte layer may comprise an electrolyte selected from a gelpolymer electrolyte using PEO, PVdF, PMMA, PVdF-HFP, PAN, or PVAc; and asolid electrolyte using PEO, polypropylene oxide (PPO), polyether imine(PEI), polyethylene sulphide (PES), or polyvinyl acetate (PVAc).

The electrolyte layer may further comprise a lithium salt, which may beselected from the group consisting of LiCl, LiBr, LiI, LiClO₄, LiBF₄,LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li,CF₃SO₃Li, (CF₃SO₂)₂NLi, lithium chloroborate, lower aliphatic lithiumcarbonate, lithium tetraphenylborate, and a mixture thereof.

The separator may be a porous polymer substrate made of apolyolefin-based polymer selected from the group consisting of ethylenehomopolymers, propylene homopolymers, ethylene-butene copolymers,ethylene-hexene copolymers, and ethylene-methacrylate copolymers; aporous polymer substrate made of a polymer selected from the groupconsisting of polyesters, polyacetals, polyamides, polycarbonates,polyimides, polyether ether ketones, polyether sulfones, polyphenyleneoxides, polyphenylene sulfides and polyethylene naphthalates; a poroussubstrate made of a mixture of inorganic particles and a binder polymer,or a separator having a porous coating layer formed on at least onesurface of the porous polymer substrate and comprising inorganicparticles and a binder polymer.

The porous polymer substrate may be a porous polymer film substrate or aporous non-woven fabric substrate.

The cable-type secondary battery may further comprise a protectioncoating surrounding the outer surface of the outer electrode.

The protection coating may be made of a polymer resin.

The polymer resin may comprise any one selected from the groupconsisting of PET, PVC, HDPE, an epoxy resin and a mixture thereof.

The protection coating may further comprise a moisture-blocking layer.

The moisture-blocking layer may be made of aluminum or aliquid-crystalline polymer.

Further, in accordance with yet still another aspect of the presentinvention, there is provided a cable-type secondary battery, comprising:a core for supplying lithium ions, which comprise an electrolyte; aninner electrode formed by being spirally wound to surround the outersurface of the core for supplying lithium ions, and wherein the innerelectrode comprises a current collector and an electrode active materiallayer; a separation layer surrounding the outer surface of the innerelectrodes to prevent a short circuit between electrodes; and an outerelectrode formed by being spirally wound to surround the outer surfaceof the separation layer, wherein the outer electrode comprises a currentcollector and an electrode active material layer, wherein at least oneof the inner electrode and the outer electrode is formed using theabove-mentioned electrode for a secondary battery according to thepresent disclosure.

Further, in accordance with yet still another aspect of the presentinvention, there is provided a cable-type secondary battery, comprising:two or more inner electrodes arranged in parallel to each other, aseparation layer surrounding the outer surface of the inner electrodesto prevent a short circuit between electrodes; and an outer electrodesurrounding the outer surface of the separation layer and formed bybeing spirally wound, wherein at least one of the inner electrode andthe outer electrode is formed using the above-mentioned electrode for asecondary battery according to the present disclosure.

Further, in accordance with yet still another aspect of the presentinvention, there is provided a cable-type secondary battery comprising:two or more cores for supplying lithium ions, which comprise anelectrolyte; two or more inner electrodes arranged in parallel to eachother, each inner electrode surrounding the outer surface of each corefor supplying lithium ions and comprising a current collector and anelectrode active material layer, a separation layer surrounding theouter surface of the inner electrodes to prevent a short circuit betweenelectrodes; and an outer electrode surrounding the outer surface of theseparation layer and formed by being spirally wound, which the outerelectrode comprises a current collector and an electrode active materiallayer, wherein at least one of the inner electrode and the outer anodeis formed using the above-mentioned electrode for a secondary batteryaccording to the present disclosure.

One or more electrodes according to the present disclosure may bespirally wound as the inner electrode.

Thus, the sheet-form electrode for a secondary battery according to thepresent disclosure has supporting layers on at least one surfacesthereof to exhibit surprisingly improved flexibility.

The supporting layers act as a buffer when intense external forces areapplied to the electrode, e.g., during the complete folding of theelectrode, to reduce crack generation in an electrode active materiallayer even though the amount of a binder in the electrode activematerial layer is not raised. Thereby, the release of the electrodeactive material layer from a current collector can be prevented.

Accordingly, the sheet-form electrode can prevent a decrease in batterycapacity and can improve the cycle life characteristic of batteries.

Also, the sheet-form electrode has a porous organic-inorganic layer onthe top surface of its electrode active material layer to allow goodintroduction of an electrolyte solution in an electrode active materiallayer, thereby inhibiting a resistance rise in the electrode.

Further, as the porous supporting layer is provided, the electrolytesolution can be impregnated into the pores of the porous supportinglayer to inhibit a resistance rise in the battery, thereby preventingthe deterioration of battery performances.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate preferred embodiments of thepresent invention and, together with the foregoing disclosure, serve toprovide further understanding of the technical spirit of the presentinvention. However, the present invention is not to be construed asbeing limited to the drawings.

FIG. 1 shows a cross-section of a sheet-form electrode for a secondarybattery according to one embodiment of the present disclosure.

FIG. 2 shows a cross-section of a sheet-form electrode for a secondarybattery according to another embodiment of the present disclosure.

FIG. 3 schematically shows a method of preparing a sheet-form electrodefor a secondary battery according to one embodiment of the presentdisclosure.

FIG. 4 shows a surface of a mesh-form current collector according to oneembodiment of the present disclosure.

FIG. 5 schematically shows a surface of a current collector having aplurality of recesses, according to one embodiment of the presentdisclosure.

FIG. 6 schematically shows a surface of a current collector having aplurality of recesses, according to another embodiment of the presentdisclosure.

FIG. 7 schematically shows a sheet-form inner electrode being wound onthe outer surface of a core for supplying lithium ions in the cable-typesecondary battery of the present disclosure.

FIG. 8 is an exploded perspective view schematically showing the insideof a cable-type secondary battery according to one embodiment of thepresent disclosure.

FIG. 9 schematically shows a cross-section of a cable-type secondarybattery having a plurality of inner electrodes according to the presentdisclosure.

<Explanation of Reference Numerals> 10: Current collector 20: Electrodeactive material layer 30: Porous organic-inorganic layer 30′: Mixedorganic- inorganic slurry 40: First supporting layer 50: Secondsupporting layer 60: Coating blade 100, 200: Cable-type secondarybattery 110, 210: Core for supplying lithium ions 120, 220: Innercurrent collector 130, 230: Inner electrode active material layer 140,240: Porous organic-inorganic layer 150, 250: First supporting layer160, 260: Second supporting layer 170, 270: Separation layer 180, 280:Outer electrode active material layer 190, 290: Outer current collector195, 295: Protection coating

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Priorto the description, it should be understood that the terms used in thespecification and the appended claims should not be construed as limitedto general and dictionary meanings, but interpreted based on themeanings and concepts corresponding to technical aspects of the presentdisclosure on the basis of the principle that the inventor is allowed todefine terms appropriately for the best explanation.

Therefore, the description proposed herein is just a preferable examplefor the purpose of illustrations only, not intended to limit the scopeof the disclosure, so it should be understood that other equivalents andmodifications could be made thereto without departing from the spiritand scope of the disclosure.

FIGS. 1 and 2 show a cross-section of a sheet-form electrode for asecondary battery according to one embodiment of the present disclosure,and FIG. 3 schematically shows a preferred method of preparing asheet-form electrode for a secondary battery according to one embodimentof the present disclosure.

Referring FIGS. 1 to 3, a sheet-form electrode for a secondary batteryaccording to the present disclosure comprises a current collector 10; anelectrode active material layer 20 formed on one surface of the currentcollector 10; a porous organic-inorganic layer 30 formed on theelectrode active material layer 20 and comprising inorganic particlesand a polymer binder, and a first porous supporting layer 40 formed onthe porous organic-inorganic layer 30.

And, the sheet-form electrode for a secondary battery according to oneembodiment of the present disclosure may comprise a second supportinglayer 50 formed on the another surface of the current collector 10

In order for a battery to have flexibility, electrodes used in thebattery should have sufficient flexibility. However, in the case ofconventional cable-type batteries being one example of flexiblebatteries, an electrode active material layer is apt to be released bystress due to external force for the shape variation, or by its rapidvolume expansion during charging and discharging processes when ahigh-capacity anode active material containing Si, Sn or the like isused. Such a release of the electrode active material layer reducesbattery capacity and deteriorates cycle life characteristics. As anattempt for overcoming this problem, the amount of a binder in theelectrode active material layer has been raised to provide flexibilityduring bending or twisting.

However, the increase of a binder amount in the electrode activematerial layer causes an electrode resistance rise to deterioratebattery performances. Also, when intense external forces are applied,for example, in the case that electrodes are completely folded, therelease of the electrode active material layer cannot be prevented eventhough the amount of a binder becomes increased. Therefore, this methodis insufficient to solve such problems.

For the purpose of overcoming the above-mentioned problems, the presentinventors have designed the electrode for a secondary battery in theform of a sheet by comprising the first supporting layer 40 formed onthe outer surface thereof, and additionally the second supporting layer50 formed on the another surface of the current collector 10.

That is, even if the electrode is applied by external forces duringbending or twisting, the first supporting layer 40 having porosity actsas a buffer capable of mitigating the external forces applied to theelectrode active material layer 20, to prevent the release of theelectrode active material layer 20, thereby improving the flexibility ofthe electrode. Also, the second supporting layer 50, which may furtherbe formed, can inhibit a short circuit of the current collector 10,thereby more improving the flexibility of the electrode.

Furthermore, the electrode of the present disclosure comprises a porousorganic-inorganic layer 30 as an adhesive for adhering the first poroussupporting layer 40 with the electrode active material layer to beintegrated with each other, the porous organic-inorganic layer 30 beingobtained by drying a slurry containing inorganic particles and a polymerbinder.

If a general binder is used as the adhesive, it acts as a resistant ofthe electrode to deteriorate battery performances. In contrast, theporous organic-inorganic layer 30 having a porous structure allows goodintroduction of an electrolyte solution in an electrode active materiallayer, thereby inhibiting a resistance rise in the electrode.Hereinafter, a method of preparing the sheet-form electrode for asecondary battery will be explained with reference to FIGS. 1 3. Foryour information, although FIG. 3 represents one case of forming aporous organic-inorganic layer after a second supporting layer 50 ispreviously formed on the under surface of the current collector 10, thisis just one embodiment of the present disclosure. Therefore, asmentioned below, a porous organic-inorganic layer may be formed in thecondition that a second supporting layer 50 is not formed.

First, a slurry (20′) containing an electrode active material is appliedon the other surface of the current collector 10, followed by drying, toform an electrode active material layer (S1).

The current collector 10 may be made of stainless steel, aluminum,nickel, titanium, sintered carbon, or copper; stainless steel treatedwith carbon, nickel, titanium or silver on the surface thereof; analuminum-cadmium alloy; a non-conductive polymer treated with aconductive material on the surface thereof; a conductive polymer; ametal paste comprising metal powders of Ni, Al, Au, Ag, Pd/Ag, Cr, Ta,Cu, Ba or ITO; or a carbon paste comprising carbon powders of graphite,carbon black or carbon nanotube.

As mentioned above, when secondary batteries are subject to externalforces by bending or twisting, an electrode active material layer may bereleased from a current collector. For this reason, large amounts ofbinder components are used in the electrode active material layer so asto provide flexibility in electrodes. However, large amounts of bindermay be easily peeled off owing to swelling by an electrolyte solution,thereby deteriorating battery performances.

Accordingly, for the purpose of improving adhesiveness between anelectrode active material layer and a current collector, the currentcollector 10 may further comprise a primer coating layer consisting of aconductive material and a binder.

The conductive material may comprise any one selected from the groupconsisting of carbon black, acetylene black, ketjen black, carbon fiber,carbon nanotube, graphene and a mixture thereof, but is not limitedthereto.

The binder may be selected from the group consisting of polyvinylidenefluoride (PVDF), polyvinylidene fluoride-co-hexafluoro propylene,polyvinylidene fluoride-co-trichloroethylene, polybutyl acrylate,polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone,polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide,polyarylate, cellulose acetate, cellulose acetate butyrate, celluloseacetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol,cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methylcellulose, styrene-butadiene rubber, acrylonitrile-styrene-butadienecopolymer, polyimide and a mixture thereof, but is not limited thereto.

Also, referring to FIGS. 4 to 6, the current collector may be in theform of a mesh, and may have a plurality of recesses on at least onesurface thereof so as to more increase its surface area. The recessesmay be continuously patterned or intermittently patterned. That is,continuous patterned recesses may be formed with spacing apart with eachother in the longitudinal direction, or a plurality of holes may beformed in the form of intermittent patterns. The plurality of holes maybe a circular or polygonal shape.

In the present disclosure, when the electrode for a secondary battery isused as an anode, the electrode active material layer may comprise anactive material selected from the group consisting of natural graphite,artificial graphite, or carbonaceous material; lithium-titanium complexoxide (LTO), and metals (Me) including Si, Sn, Li, Zn, Mg, Cd, Ce, Niand Fe; alloys of the metals; an oxide (MeOx) of the metals; a complexof the metals and carbon; and a mixture thereof, and when the electrodefor a secondary battery is used as a cathode, the electrode activematerial layer may comprise an active material selected from the groupconsisting of LiCoO₂, LiNiO₂, LiMn₂O₄, LiCoPO₄, LiFePO₄, LiNiMnCoO₂,LiNi_(1-x-y-z)Co_(x)M1_(y)M2_(z)O₂ (wherein M1 and M2 are eachindependently selected from the group consisting of Al, Ni, Co, Fe, Mn,V, Cr, Ti, W, Ta, Mg and Mo, and x, y and z are each independently anatomic fraction of oxide-forming elements, in which 0≦x<0.5, 0≦y<0.5,0≦z<0.5, and x+y+z≦1), and a mixture thereof.

Then, a slurry (30′) containing inorganic particles and a polymer binderis applied on the electrode active material layer 20 (S2).

The mixed organic-inorganic slurry (30′) is used as an adhesive. If onlya general adhesive is used as the adhesive, it fails to form pores,making it difficult for an electrolyte solution to be introduced in theelectrode active material layer, and therefore acts as a resistant ofthe electrode to deteriorate battery performances.

The mixed organic-inorganic slurry (30′) forms a porousorganic-inorganic layer 30 later, and it is obtained by mixing theinorganic particles and the polymer binder in a weight ratio of 20:80 to95:5.

The inorganic particles may be inorganic particles having a dielectricconstant of 5 or higher, inorganic particles having the ability totransport lithium ions, or a mixture thereof.

Examples of the inorganic particles having a dielectric constant of 5 orhigher include BaTiO₃, Pb(Zr_(x)Ti_(1-x))O₃(PZT, 0<x<1),Pb_(1-x)La_(x)Zr_(1-y)Ti_(y)O₃ (PLZT, 0<x<1, 0<y<1),(1-x)Pb(Mg_(1/3)Nb_(2/3))O₃-xPbTiO₃ (PMN-PT, 0<x<1), hafnia (HfO₂),SrTiO₃, SnO₂, CeO₂, MgO, NiO, CaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, SiC, SiO₂,AlOOH, Al(OH)₃, TiO₂ and a mixture thereof.

Also, examples of the inorganic particles having the ability totransport lithium ions include lithium phosphate (Li₃PO₄), lithiumtitanium phosphate (Li_(x)Ti_(y)(PO₄)₃, 0<x<2, 0<y<3), lithium aluminumtitanium phosphate (Li_(x)Al_(y)Ti_(z)(PO₄)₃, 0<x<2, 0<y<1, 0<z<3),(LiAlTiP)_(x)O_(y) type glass (0<x<4, 0<y<13), lithium lanthanumtitanate (Li_(x)La_(y)TiO₃, 0<x<2, 0<y<3), lithium germaniumthiophosphate (Li_(x)Ge_(y)P_(z)S_(w), 0<x<4, 0<y<1, 0<z<1, 0<w<5),lithium nitride (Li_(x)N_(y), 0<x<4, 0<y<2), SiS₂ type glass(Li_(x)Si_(y)S_(z), 0<x<3, 0<y<2, 0<z<4), P₂S₅ type glass(Li_(x)P_(y)S_(z), 0<x<3, 0<y<3, 0<z<7) inorganic particles, and amixture thereof.

The inorganic particles may have an average diameter of 10 nm to 5 μm.

Also, the polymer binder may be selected from the group consisting ofpolyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polybutylacrylate, polymethyl methacrylate, polyacrylonitrile,polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate,polyethylene oxide, polyarylate, cellulose acetate, cellulose acetatebutyrate, cellulose acetate propionate, cyanoethylpullulan,cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose,pullulan, carboxyl methyl cellulose, styrene-butadiene rubber,acrylonitrile-styrene-butadiene copolymer, polyimide and a mixturethereof, but is not limited thereto.

Then a first porous supporting layer 40 is placed on the slurry which isapplied as the above-mentioned (30′)

Meanwhile, the first supporting layer 40 may be a mesh-form porousmembrane or a non-woven fabric. Such a porous structure allows goodintroduction of an electrolyte solution in the electrode active materiallayer 20, and also the first supporting layer 40 itself has superiorimpregnation of the electrolyte solution to provide good ionicconductivity, thereby preventing an electrode resistance rise andeventually preventing the deterioration of battery performances.

The first supporting layer 40 may be made of any one selected from thegroup consisting of high-density polyethylene, low-density polyethylene,linear low-density polyethylene, ultra-high molecular weightpolyethylene, polypropylene, polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate,polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide,polyphenylene sulfide, polyethylene naphthalate, and a mixture thereof.

Also, the first supporting layer 40 may further comprise a conductivematerial-coating layer having a conductive material and a binder on thetop surface thereof. The conductive material-coating layer functions toimprove the conductivity of an electrode active material layer andreduce electrode resistance, thereby preventing the deterioration ofbattery performances.

The conductive material and the binder used in the conductivematerial-coating layer may be the same as those used in the primercoating layer, which are mentioned above.

Such conductive material-coating layer is more favorable when applied ina cathode because a cathode active material layer has low conductivityto intensify performance deterioration due to electrode resistance rise,than in an anode whose active material layer has relatively goodconductivity and thus is not largely affected by the conductivematerial-coating layer to exhibit performances similar to conventionalanodes.

In the conductive material-coating layer, the conductive material andthe binder may be present in a weight ratio of 80:20 to 99:1. The use oflarge amounts of binder may induce a severe rise in electroderesistance. Therefore, when such a numerical range is satisfied,electrode resistance can be prevented from its severe rise. Also, asmentioned above, since the first supporting layer acts as a buffer whichcan prevent the release of an electrode active material layer, electrodeflexibility is not largely affected by the use of the binder in arelative small amount.

Subsequently, the resultant obtained in step (S3) is compressed to forma porous organic-inorganic layer 30 which is adhered between theelectrode active material layer 20 and the first supporting layer 40 tobe integrated with each other (S4).

The porous organic-inorganic layer 30 may have a porous structure forgood introduction of an electrolyte solution in an electrode activematerial layer, and have a pore size of 0.01 to 10 μm and a porosity of5 to 95%.

The porous coating layer may be formed to have a porous structurethrough phase separation or phase change by a non-solvent during itspreparation, or may be formed by interstitial volumes between theinorganic particles, the interstitial volumes being generated from thestate that the inorganic particles are connected and immobilized by thepolymer binder.

Meanwhile, if the porous organic-inorganic layer 30 is formed by coatingthe mixed organic-inorganic slurry (30′) on one surface of the electrodeactive material layer 20, followed by drying, and then the firstsupporting layer 40 is formed by lamination thereon, the bindercomponent in the slurry (30′) for adhering the electrode active materiallayer 20 with the first supporting layer 40 may be cured, making itdifficult to maintain strong adhesion between such two layers.

Also, unlike the preferred preparation method of the present disclosurewhich uses the first porous supporting layer prepared in advance, if aporous supporting layer is formed by coating a polymer solution on theporous organic-inorganic layer, such a porous supporting layer formed bycoating the polymer solution has poor mechanical properties than thoseof the first porous supporting layer of the present disclosure, therebyfailing to effectively prevent the release of the electrode activematerial layer.

In contrast, according to the preferred preparation method of thepresent disclosure, in the case that the first supporting layer 40 isplaced on the top of the mixed organic-inorganic slurry (30′) before thebinder component is cured, and then these are together coated by meansof a coating blade 60, thereby forming the porous organic-inorganiclayer 30 adhered between the electrode active material layer 20 and thefirst supporting layer 40 to be integrated with each other.

Meanwhile, the method according to one embodiment of the presentdisclosure may comprise forming a second supporting layer (50) bycompression on another surface of a current collector; before the (S1)step or after the (S4) step. The second supporting layer (50) caninhibit a short circuit of the current collector 10.

Meanwhile, the second supporting layer 50 may be a polymer film whichmay be made of any one selected from the group consisting of polyolefin,polyester, polyimide, polyamide and a mixture thereof. In addition, thepresent disclosure provides a secondary battery comprising a cathode, ananode, a separator interposed between the cathode and the anode, and anon-aqueous electrolyte solution, wherein at least one of the cathodeand the anode is the above-mentioned electrode for a secondary battery.

The secondary battery of the present disclosure may be in the generalform of stacking, winding or stacking/folding, and also it may be in theparticular form of cable type.

Meanwhile, a cable-type secondary battery according to one aspect of thepresent disclosure comprises an inner electrode; a separation layersurrounding the outer surface of the inner electrode to prevent a shortcircuit between electrodes; and an outer electrode surrounding the outersurface of the separation layer and formed by being spirally wound,wherein at least one of the inner electrode and the outer electrode isformed using the electrode according to one embodiment of the presentdisclosure

The term ‘spirally’ used herein refers to represent a helix shape thatturns around at a certain area while moving, including general springforms.

The outer electrode may be in the form of a uniaxially extended strip.

Also, the outer electrode may be spirally wound so that it is notoverlapped in its width or overlapped in its width. For example, inorder to prevent the deterioration of battery performances, thesheet-form outer electrode may be spirally wound with space within thedouble length of its width so that it is not overlapped.

Alternatively, the outer electrode may be spirally wound whileoverlapping in its width. In this case, in order to inhibit an excessiveresistance rise within the battery, the sheet-form outer electrode maybe spirally wound so that the width of its overlapped part may be within0.9 folds of the width of the sheet-form outer electrode itself.

The inner electrode may be a hollow structure whose central part isempty.

The inner current collector comprised in the inner electrode may be oneor more wires being spirally wound or one or more sheets being spirallywound.

Alternatively, the inner current collector may be two or more wiresbeing spirally crossed with each other.

Also, the inner electrode may be provided with a core of inner currentcollector therein.

The core of inner current collector may be made of carbon nanotube,stainless steel, aluminum, nickel, titanium, sintered carbon, or copper;stainless steel treated with carbon, nickel, titanium or silver on thesurface thereof; an aluminum-cadmium alloy; a non-conductive polymertreated with a conductive material on the surface thereof; a conductivepolymer.

Alternatively, the inner electrode may be provided with a core forsupplying lithium ions, which comprises an electrolyte therein.

The core for supplying lithium ions may comprise a gel polymerelectrolyte and a support.

Also, the core for supplying lithium ions may comprise a liquidelectrolyte and a porous carrier.

Alternatively, the inner electrode may be provided with a filling coretherein.

The filling core may be made of several materials for improving variousperformances of cable-type batteries, for example polymer resins, rubberand inorganics, besides materials forming the core of inner currentcollector and the core for supplying lithium ions, and also may havevarious forms including wire, fiber, powder, mesh and foam. Meanwhile,FIG. 7 schematically shows a cable-type secondary battery according toone embodiment of the present disclosure in which a sheet-form innerelectrode is wound on the outer surface of a core 110 for supplyinglithium ions. The sheet-form inner electrode may be applied incable-type secondary batteries as shown in FIG. 6, and also thesheet-form outer electrode may be similarly wound on the outer surfaceof a separation layer.

Such a cable-type secondary battery according to one embodiment of thepresent disclosure comprises a core for supplying lithium ions, whichcomprises an electrolyte; an inner electrode surrounding the outersurface of the core for supplying lithium ions and comprising a currentcollector and an electrode active material layer, a separation layersurrounding the outer surface of the inner electrode to prevent a shortcircuit between electrodes; and an outer electrode surrounding the outersurface of the separation layer and formed by being spirally wound,which comprises a current collector and an electrode active materiallayer, wherein at least one of the inner electrode and the outer anodeis the above-mentioned electrode for a secondary battery according tothe present disclosure.

The term ‘a predetermined shape’ used herein is not limited to anyparticular shape, and refers to any shape that does not damage thenature of the present disclosure. The cable-type secondary batteryaccording to one embodiment of the present disclosure may have ahorizontal cross section of a predetermined shape, a linear structure,which extends in the longitudinal direction. The cable-type secondarybattery according to one embodiment of the present disclosure may haveflexibility, so it can freely change in shape.

Among cable-type secondary batteries which can be designed by thepresent disclosure, a cable-type secondary battery 100 in which theabove-mentioned electrode for a secondary battery is used as an innerelectrode is shown in FIG. 8.

Referring to FIG. 8, the cable-type secondary battery 100 comprises acore 110 for supplying lithium ions, which comprises an electrolyte; aninner electrode surrounding the outer surface of the core 110 forsupplying lithium ions; a separation layer 170 surrounding the outersurface of the inner electrode to prevent a short circuit betweenelectrodes; and an outer electrode formed by being spirally wound tosurround the outer surface of the separation layer 170 and comprising anouter current collector 190 and an outer electrode active material layer180, wherein the inner electrode comprises an inner current collector120, an inner electrode active material layer 130 formed on one surfaceof the inner current collector 120, a porous organic-inorganic layer 140formed on the top surface of the inner electrode active material layer130 and comprising inorganic particles and a polymer binder, a firstporous supporting layer 150 formed on the top surface of the porousorganic-inorganic layer 140, and a second supporting layer 160 formed onthe other surface of the inner current collector 120. As alreadymentioned above, the sheet-form electrode for a secondary batteryaccording to the present disclosure may be used as the outer electrode,not the inner electrode, or may be used as both of them.

The core 110 for supplying lithium ions comprises an electrolyte whichis not particularly limited to its kinds and may be selected from anon-aqueous electrolyte solution using ethylene carbonate (EC),propylene carbonate (PC), butylenes carbonate (BC), vinylene carbonate(VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methylcarbonate (EMC), methyl formate (MF), γ-butyrolactone (γ-BL), sulfolane,methyl acetate (MA) or methyl propionate (MP); a gel polymer electrolyteusing PEO, PVdF, PVdF-HFP, PMMA, PAN, or PVAc; and a solid electrolyteusing PEO, polypropylene oxide (PPO), polyether imine (PEI),polyethylene sulphide (PES), or polyvinyl acetate (PVAc). Also, theelectrolyte may further comprise a lithium salt which may be selectedfrom LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃,LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, (CF₃SO₂)₂NLi,lithium chloroborate, lower aliphatic lithium carbonate, lithiumtetraphenylborate, and a mixture thereof. The core 110 for supplyinglithium ions may consist of only an electrolyte, and especially a liquidelectrolyte may be formed by using a porous carrier.

In the present disclosure, the inner electrode may be an anode or acathode, and the outer electrode may be a cathode or an anodecorresponding to the inner electrode.

Electrode active materials which may be used in the anode and thecathode are the same as those which are mentioned above.

Meanwhile, the separation layer may be an electrolyte layer or aseparator.

The electrolyte layer serving as an ion channel may be made of agel-type polymer electrolyte using PEO, PVdF, PVdF-HFP, PMMA, PAN orPVAc, or a solid electrolyte using PEO, polypropylene oxide (PPO),polyethylene imine (PEI), polyethylene sulfide (PES) or polyvinylacetate (PVAc). The matrix of the solid electrolyte is preferably formedusing a polymer or a ceramic glass as the backbone. In the case oftypical polymer electrolytes, the ions move very slowly in terms ofreaction rate, even when the ionic conductivity is satisfied. Thus, thegel-type polymer electrolyte which facilitates the movement of ions ispreferably used compared to the solid electrolyte. The gel-type polymerelectrolyte has poor mechanical properties and thus may comprise asupport to improve poor mechanical properties, and a porous support or across-linked polymer may be used as such support. The electrolyte layerof the present invention can serve as a separator, and thus anadditional separator may be omitted.

In the present disclosure, the electrolyte layer may further comprise alithium salt. The lithium salt can improve an ionic conductivity andresponse time. Non-limiting examples of the lithium salt may includeLiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂,LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li, (CF₃SO₂)₂NLi, lithiumchloroborate, lower aliphatic lithium carbonate, and lithiumtetraphenylborate.

Examples of the separator may include, but is not limited to, a porouspolymer substrate made of a polyolefin-based polymer selected from thegroup consisting of ethylene homopolymers, propylene homopolymers,ethylene-butene copolymers, ethylene-hexene copolymers, andethylene-methacrylate copolymers; a porous substrate made of a polymerselected from the group consisting of polyesters, polyacetals,polyamides, polycarbonates, polyimides, polyether ether ketones,polyether sulfones, polyphenylene oxides, polyphenylene sulfides andpolyethylene naphthalates; a porous polymer substrate made of a mixtureof inorganic particles and a binder polymer; or a separator having aporous coating layer formed on at least one surface of the porouspolymer substrate and comprising inorganic particles and a binderpolymer.

In the porous coating layer formed from inorganic particles and a binderpolymer, the inorganic particles are bound to each other by the binderpolymer (i.e., the binder polymer connects and immobilizes the inorganicparticles), and also the porous coating layer maintains the state ofbinding with the first supporting layer by the binder polymer, In such aporous coating layer, the inorganic particles are filled in contact witheach other, from which interstitial volumes are formed between theinorganic particles. The interstitial volumes between the inorganicparticles become empty spaces to form pores.

Among these, in order for the lithium ions of the core for supplyinglithium ions to be transferred to the outer electrode, it is preferredto use a non-woven fabric separator corresponding to the poroussubstrate made of a polymer selected from the group consisting ofpolyesters, polyacetals, polyamides, polycarbonates, polyimides,polyether ether ketones, polyether sulfones, polyphenylene oxides,polyphenylene sulfides and polyethylene naphthalates.

Also, the cable-type secondary battery of the present disclosure has aprotection coating 195. The protection coating 195 acts as an insulatorand is formed to surround the outer current collector, therebyprotecting the electrodes against moisture in the air and externalimpacts. The protection coating may be made of conventional polymerresins having a moisture-blocking layer. The moisture-blocking layer maybe made of aluminum or a liquid-crystalline polymer which have goodwater-blocking ability, and the polymer resins may be PET, PVC, HDPE orepoxy resins.

Further, a cable-type secondary battery according to one aspect of thepresent disclosure comprises: two or more inner electrodes arranged inparallel to each other; a separation layer surrounding the outer surfaceof the inner electrodes to prevent a short circuit between electrodes;and an outer electrode surrounding the outer surface of the separationlayer and formed by being spirally wound, wherein at least one of theinner electrode and the outer electrode is formed using theabove-mentioned electrode for a secondary battery according to thepresent disclosure.

Further a cable-type secondary battery according to one aspect of thepresent disclosure comprises: two or more cores for supplying lithiumions, which comprise an electrolyte; two or more inner electrodesarranged in parallel to each other, each inner electrode surrounding theouter surface of each core for supplying lithium ions and comprising acurrent collector and an electrode active material layer; a separationlayer surrounding the outer surface of the inner electrodes to prevent ashort circuit between electrodes; and an outer electrode surrounding theouter surface of the separation layer and formed by being spirallywound, which the outer electrode comprises a current collector and anelectrode active material layer, wherein at least one of the innerelectrode and the outer anode is formed using the above-mentionedelectrode for a secondary battery according to the present disclosure.

Among cable-type secondary batteries having two or more inner electrodeswhich can be designed by the present disclosure, a cable-type secondarybattery 200 in which the above-mentioned electrode for a secondarybattery is used as an inner electrode is shown in FIG. 9.

Referring to FIG. 9, the cable-type secondary battery 200 comprises twoor more cores 210 for supplying lithium ions, which comprise anelectrolyte; two or more inner electrodes arranged in parallel to eachother, each inner electrode surrounding the outer surface of each corefor supplying lithium ions; a separation layer 270 surrounding the outersurface of the inner electrodes to prevent a short circuit betweenelectrodes; and an outer electrode surrounding the outer surface of theseparation layer 270 and formed by being spirally wound, which the outerelectrode comprises an outer current collector 290 and an outerelectrode active material layer 280, wherein each inner electrodecomprises an inner current collector 220, an inner electrode activematerial layer 230 formed on one surface of the inner current collector220, a porous organic-inorganic layer 240 formed on the top surface ofthe inner electrode active material layer 230 and comprising inorganicparticles and a polymer binder, a first porous supporting layer 250formed on the top surface of the porous organic-inorganic layer 240, anda second supporting layer 260 formed on the other surface of the innercurrent collector 220.

As already mentioned above, the sheet-form electrode for a secondarybattery according to the present disclosure may be used as the outerelectrode, not the inner electrode, or may be used as both of them.

In the cable-type secondary battery 200 which has a plurality of innerelectrodes, the number of the inner electrodes can be adjusted tocontrol the loading amount of the electrode active material layers aswell as battery capacity, and a probability of short circuit can beprevented owing to the presence of multiple electrodes.

APPLICABILITY TO THE INDUSTRY

The present disclosure has been described in detail. However, it shouldbe understood that the detailed description and specific examples, whileindicating preferred embodiments of the disclosure, are given by way ofillustration only, since various changes and modifications within thespirit and scope of the disclosure will become apparent to those skilledin the art from this detailed description.

What is claimed is:
 1. A cable-type secondary battery, comprising: aninner electrode; a separation layer surrounding an outer surface of theinner electrode to prevent a short circuit between electrodes; and anouter electrode surrounding an outer surface of the separation layer andformed by being helically wound, wherein at least one of the innerelectrode and the outer electrode is formed using a sheet-form electrodefor a secondary battery, comprising a current collector, an electrodeactive material layer formed on one surface of the current collector, aporous organic-inorganic layer formed on the electrode active materiallayer and comprising inorganic particles and a polymer binder, and afirst porous supporting layer formed on the porous organic-inorganiclayer.
 2. The cable-type secondary battery according to claim 1, whereinthe outer electrode is in the form of a uniaxially extended strip. 3.The cable-type secondary battery according to claim 1, wherein the outerelectrode is helically wound so that it does not overlap itself.
 4. Thecable-type secondary battery according to claim 3, wherein the outerelectrode is helically wound so that each pass of its helical winding isseparated by a space.
 5. The cable-type secondary battery according toclaim 1, wherein the outer electrode is helically wound so that itoverlaps itself.
 6. The cable-type secondary battery according to claim5, wherein the outer electrode is helically wound so that a width of itsoverlapped part is less than or equal to 90% of a width of the outerelectrode.
 7. The cable-type secondary battery according to claim 1,wherein the inner electrode is a hollow structure whose central part isempty.
 8. The cable-type secondary battery according to claim 7, whereinthe inner electrode comprises one or more electrodes for a secondarybattery being helically wound.
 9. The cable-type secondary batteryaccording to claim 7, wherein the inner electrode is provided with acore of inner current collector, a core for supplying lithium ions,which comprises an electrolyte, or a filling core therein.
 10. Thecable-type secondary battery according to claim 9, wherein the core ofinner current collector is made of carbon nanotube, stainless steel,aluminum, nickel, titanium, sintered carbon, or copper; stainless steeltreated with carbon, nickel, titanium or silver on a surface thereof; analuminum-cadmium alloy; a non-conductive polymer treated with aconductive material on a surface thereof; or a conductive polymer. 11.The cable-type secondary battery according to claim 9, wherein the corefor supplying lithium ions comprises a gel polymer electrolyte and asupport.
 12. The cable-type secondary battery according to claim 9,wherein the core for supplying lithium ions comprises a liquidelectrolyte and a porous carrier.
 13. The cable-type secondary batteryaccording to claim 9, wherein the electrolyte is selected from anon-aqueous electrolyte solution using ethylene carbonate (EC),propylene carbonate (PC), butylenes carbonate (BC), vinylene carbonate(VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methylcarbonate (EMC), methyl formate (MF), γ-butyrolactone (γ-BL), sulfolane,methyl acetate (MA) or methyl propionate (MP); a gel polymer electrolyteusing PEO, PVdF, PVdF-HFP, PMMA, PAN, or PVAc; and a solid electrolyteusing PEO, polypropylene oxide (PPO), polyether imine (PEI),polyethylene sulphide (PES), or polyvinyl acetate (PVAc).
 14. Thecable-type secondary battery according to claim 9, wherein theelectrolyte further comprises a lithium salt.
 15. The cable-typesecondary battery according to claim 14, wherein the lithium salt isselected from LiCl, LiBr, LiI, LiClO₄, LiBF₄, LiB₁₀Cl₁₀, LiPF₆,LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li, CF₃SO₃Li,(CF₃SO₂)₂NLi, lithium chloroborate, lower aliphatic lithium carbonate,lithium tetraphenylborate, and a mixture thereof.
 16. The cable-typesecondary battery according to claim 9, wherein the filling core is madeof polymer resins, rubber and inorganics in the form of a wire, a fiber,a powder, a mesh or a foam.
 17. The cable-type secondary batteryaccording to claim 1, wherein the inner electrode is an anode or acathode, and the outer electrode is a cathode or an anode correspondingto the inner electrode.
 18. The cable-type secondary battery accordingto claim 1, wherein the separation layer is an electrolyte layer or aseparator.
 19. The cable-type secondary battery according to claim 18,wherein the electrolyte layer comprises an electrolyte selected from agel polymer electrolyte using PEO, PVdF, PMMA, PVdF-HFP, PAN, or PVAc;and a solid electrolyte using PEO, polypropylene oxide (PPO), polyetherimine (PEI), polyethylene sulphide (PES), or polyvinyl acetate (PVAc).20. The cable-type secondary battery according to claim 18, wherein theelectrolyte layer further comprises a lithium salt.
 21. The cable-typesecondary battery according to claim 20, wherein the lithium salt isselected from the group consisting of LiCl, LiBr, LiI, LiClO₄, LiBF₄,LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li,CF₃SO₃Li, (CF₃SO₂)₂NLi, lithium chloroborate, lower aliphatic lithiumcarbonate, lithium tetraphenylborate, and a mixture thereof.
 22. Thecable-type secondary battery according to claim 18, wherein theseparator is a porous polymer substrate made of a polyolefin-basedpolymer selected from the group consisting of ethylene homopolymers,propylene homopolymers, ethylene-butene copolymers, ethylene-hexenecopolymers, and ethylene-methacrylate copolymers; a porous polymersubstrate made of a polymer selected from the group consisting ofpolyesters, polyacetals, polyamides, polycarbonates, polyimides,polyether ether ketones, polyether sulfones, polyphenylene oxides,polyphenylene sulfides and polyethylene naphthalates; a porous substratemade of a mixture of inorganic particles and a binder polymer; or aseparator having a porous coating layer formed on at least one surfaceof the porous polymer substrate and comprising inorganic particles and abinder polymer.
 23. The cable-type secondary battery according to claim22, wherein the porous polymer substrate is a porous polymer filmsubstrate or a porous non-woven fabric substrate.
 24. The cable-typesecondary battery according to claim 1, which further comprises aprotection coating surrounding an outer surface of the outer electrode.25. The cable-type secondary battery according to claim 24, wherein theprotection coating is made of a polymer resin.
 26. The cable-typesecondary battery according to claim 25, wherein the polymer resincomprises any one selected from the group consisting of PET, PVC, HDPE,an epoxy resin and a mixture thereof.
 27. The cable-type secondarybattery according to claim 25, wherein the protection coating furthercomprises a moisture-blocking layer.
 28. The cable-type secondarybattery according to claim 27, wherein the moisture-blocking layer ismade of aluminum or a liquid-crystalline polymer.
 29. A cable-typesecondary battery, comprising: two or more inner electrodes arranged inparallel to each other; a separation layer surrounding respective outersurfaces of the two or more inner electrodes to prevent a short circuitbetween electrodes; and an outer electrode surrounding an outer surfaceof the separation layer and formed by being helically wound, wherein atleast one of the two or more inner electrodes and the outer electrode isformed using a sheet-form electrode for a secondary battery, comprisinga current collector, an electrode active material layer formed on onesurface of the current collector, a porous organic-inorganic layerformed on the electrode active material layer and comprising inorganicparticles and a polymer binder, and a first porous supporting layerformed on the porous organic-inorganic layer.